I was looking at a couple of charging ICs (BQ2002 for instance) and some of the fast charger ICs can charge up to 2A whilst running of a 5v supply. In this case charging a empty 1v NiMH cell means that 4v * 2A ~ 8w is being dissipated by the IC? Do they use some kind of internal buck converter to step the voltage down?

  • \$\begingroup\$ I don't think those have an integrated buck converter. The IC is too small to house an inductor. I also don't see anywhere in the BQ2002 datasheet that says 2A. \$\endgroup\$ – DKNguyen May 7 '19 at 19:15
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    \$\begingroup\$ A BQ2002 is a Fast-Change Management IC. It doesn't itself pass the charge current - it just controls some external component(s). \$\endgroup\$ – brhans May 7 '19 at 19:18
  • \$\begingroup\$ Read around P 18 of 93. This Power IC selection guide has all types of battery chargers not just the ones in these answers ti.com/lit/pdf/slvt145 BQ2002 is current limited to 2C and others are pulse, linear etc \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 May 7 '19 at 19:30

BQ2002 and similar ICs don't actually see the charging current path through them. They are just controllers, they don't regulate by themselves. They have an output (the CC pin) which is used to indirectly control the external, high-current passing element.

You can have a look to a reference design provided by TI. The CC output controls a LM317 which is used as the regulating element (where the thermal considerations indeed apply).

This way, you can have a much greater flexibility in your design (use whatever regulator you want, linear or switched, with whatever specs you need for your specific case).

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  • \$\begingroup\$ Thank you for the clear explanation \$\endgroup\$ – user1247060 May 7 '19 at 23:40

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